The present invention relates to a water quality control method, and a method and apparatus for measuring an electrical conductivity used in the water quality control. In particular, the present invention relates to water quality control of high temperature water in atomic and thermal power plants, detection of the corrosion rate of a metallic structural member disposed in the aqueous solution in the plants, and to a method and apparatus for measuring electrical conductivity used in the detection of the corrosion rate.
Minute amount of impurities contained in high temperature water affect the corrosion of an analytical metallic material. Accordingly in atomic and thermal power plants, the high temperature water is sampled, and after cooling down and reducing the pressure, electrical conductivity is continuously monitored at room temperature to achieve the water quality control so that the measured value of the room temperature electrical conductivity does not exceed a tolerance value. Specifically, in the prior art, a room temperature electrical conductivity measuring method has been applied for the purpose of continuous monitoring of a corrosive environment and continuous monitoring of inclusion of impurities. Such a water quality control method using the room temperature electrical conductivity measuring apparatus is proposed in Japanese Patent Laid-Open Publication No. 59-60293 (1984).
However, in the method mentioned above, it is difficult to accurately evaluate the high temperature electrical conductivity at corrosive environment temperatures based on the measured values at room temperature because the dissociation of the water per se or the dissociation of the impurities, and the mobility of ions have respectively different temperature dependencies. As a result, in the prior art high temperature water quality control method using the room temperature electrical conductivity, the setting of a standard value for the water quality control is empirical, and the setting of a generally applicable and rational standard value is difficult. Furthermore, even when the room temperature electrical conductivity is the same, since the effect on the corrosion rate in high temperature water differs significantly depending on the chemical form of contained impurities, a problem is involved in that the setting of the standard value for the control of the room temperature electrical conductivity becomes more severe than needed.
Additionally, in the prior art method, the analyzing operation in the analysis of a chemical form of impurities is conducted on the off-line basis, and thus, the analyzing time becomes long. Consequently, it is difficult to detect rapidly formed impurity substances when the water quality is changed abruptly. In particular, it is difficult to detect Cl ion which accelerates the corrosion in high temperature water peculiarly, and to diagnose the cause of the abnormalities.